This invention relates to an integrated movement sensor within a micro electro-mechanical (MEM) device. The invention has application in ink ejection nozzles of the type that are fabricated by integrating the technologies applicable to micro electro-mechanical systems (MEMS) and complementary metal-oxide semiconductor (xe2x80x9cCMOSxe2x80x9d) integrated circuits, and the invention is hereinafter described in the context of that application. However, it will be understood that the invention does have broader application, to a movement sensor within various types of MEM devices.
A high speed pagewidth inkjet printer has recently been developed by the present Applicant. This typically employs in the order of 51200 inkjet nozzles to print on A4 size paper to provide photographic quality image printing at 1600 dpi. In order to achieve this nozzle density, the nozzles are fabricated by integrating MEMS-CMOS technology and in this context reference may be made to International Patent Application No. PCT/AU00/00338 by the present Applicant entitled xe2x80x9cThermal Actuatorxe2x80x9d, which corresponds to U.S. patent application Ser. No. to be advised.
A difficulty that flows from the fabrication of such a printer is that there is no convenient way of ensuring that all nozzles that extend across the printhead or, indeed, that are located on a given chip will perform identically, and this problem is exacerbated when chips that are obtained from different wafers may need to be assembled into a given printhead. Also, having fabricated a complete printhead from a plurality of chips, it is difficult to determine the energy level required for actuating individual nozzles and for evaluating the continuing performance of a given nozzle.
The present invention may be defined broadly as providing a micro electro-mechanical device comprising:
a support structure,
an actuating arm having a first end coupled to the support structure and a second end that is movable with respect to the support structure, the actuating arm being formed in part from an electrically resistive material and being arranged to conduct heat inducing electrical current from a current source within the support structure to effect movement of the actuating arm, and
a movement sensor incorporated in the device.
The movement sensor comprises
a moving contact element formed integrally with the actuating arm adjacent the second end of the actuating arm,
a fixed contact element formed integrally with the support structure and positioned to be contacted by the moving contact element when the actuating arm moves to a predetermined extent under the influence of the heat inducing electrical current, and
electrical circuit elements formed within the support structure for detecting contact between the fixed contact element and the moving contact element
The above defined arrangement permits evaluation of the operation of the actuating arm and, hence, evaluation of the operation, function and performance of the complete MEM device.
The MEM device preferably is in the form of a liquid ejector and most preferably is in the form of an ink ejection nozzle that is operable to eject an ink droplet upon actuation of the actuating arm. In this latter preferred form of the invention, the second end of the actuating arm preferably is coupled to an integrally formed paddle which is employed to displace ink from a chamber into which the actuating arm extends.
The actuating arm most preferably is formed from two similarly shaped arm portions which are interconnected in interlapping relationship. In this embodiment of the invention, a first of the arm portions is connected to a current supply and is arranged in use to be heated by current flow. However, the second arm portion functions to restrain linear expansion of the actuating arm as a complete unit and heat induced elongation of the first arm portion causes bending to occur along the length of the actuating arm. Thus, the actuating arm is effectively caused to pivot with respect to the substrate with heating and cooling of the first portion of the actuating arm.
The invention will be more fully understood from the following description of a preferred embodiment of an inkjet nozzle as illustrated in the accompanying drawings.